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WTFAQ: Your Questions Answered!

BRAKES

Here at FC we're often asked technical stuff via the mediums of email, Facebook, and being shouted at in the local Maccie Ds. Now obviously we are pretty amazing but, contrary to popular belief, we don't know absolutely everything about everything. Luckily though, we happen to have a team of industry experts on hand to deal with the really tricky stuff. This month we head over to Taiwan to ask Dan Newton, boss of PB Brakes, all your questions about stoppers...

Q. Why do people fit braided hoses? What do they do?

A. Braided hoses comprise of a Teflon inner wall, with strands of stainless steel braided on the outside for increased durability. One advantage is that they expand a lot less than your OEM rubber hoses, which allows you a much firmer brake pedal. A firmer brake pedal means more feedback and ultimately better braking. The other big advantage is safety. They're almost bulletproof! Useful if you have problems with people sabotaging your brake lines as you sleep.

Q. Why are bigger discs better than smaller discs?

A. One word: torque! When you increase the diameter of the disc, the amount of braking torque also exponentially increases. So in theory, the bigger the disc, the faster you'll stop. However, there is a limit to how big you can go. You're limited by how much grip your tyres allow. Once your discs are over a certain size you'll brake so hard that the ABS will initiate in order to prevent the tyres from losing traction, and whatever gains you made are out the window. Brake pads can also be a limiting factor as your bog-standard street compound will just melt if subjected to more torque than it can handle. You also need to consider that brake discs are fairly heavy items, and increasing the weight that each wheel needs to rotate is going to have a noticeable effect on your acceleration. This maximum recommend size of discs depends on the car, but generally speaking, heavier cars require larger discs for effective braking, and lighter cars can get away with running smaller discs.

Q. Why do performance brake discs have grooves and holes in them?

A. There are a couple of reasons for having drilled holes or slots (or both) in your brake discs. The friction created between pads and disc produces a lot of heat, which leads to brake fade. The holes and grooves help heat escape and keep the discs nice and cool. They also help to channel water and other unwanted material away from the contact surface to maintain maximum friction. The discs are actually cast plain, then once they've been milled down to a smooth surface the pattern is engraved onto them by CNC machines. The pattern on most brake discs flows in the same direction as the internal veins, which reduces the strength of the discs. Ours flow in the opposite direction, as we found this doesn't decrease the strength as much without affecting the function.

Q. Why is it important to change your brake fluid regularly?

A. Glycol-based brake fluid is hydroscopic, so it loves to absorb moisture, which is always going to find a way into the brake system via micro-pores in the cap, lines and seals. This is a bad thing as it dramatically reduces the boiling temperature of the brake fluid — three per cent water in DOT4 fluid can reduce the boiling point by up to 50 percent! That's dangerous because bubbles are compressible, which causes at best a spongy pedal feeling, and in extreme cases it may go all the way to the floor without actually stopping the car!

Q. Why are some rotors one-piece and others two-piece?

A. It all comes down to cost really. Your bog-standard OEM discs are usually cast in one solid piece as it's the most cost-effective way to manufacture them. One-piece discs are fine for popping down the shops to pick up some milk, but push them too hard or take them on the track and they will fade within a couple of laps at race speed. When you're flying down the straight at 130mph and you hit the brake pedal, the last thing you want is for it to sink right down to the floor because of fade. The best solution is to upgrade to a set of two-piece discs with billet aluminium centre caps. The contact area between the actual disc and centre cap is minimal, which greatly improves heat dissipation by allowing the heat to escape, whereas one-piece discs tend to retain it. Another advantage of having centre caps is aluminium dissipates heat more effectively than steel, and it's a lot lighter too. The next step up would be two-piece floating rotors. The centre caps on these bad boys have even less contact area with the disc, allowing ridiculously efficient cooling! A little bit of an overkill for most street cars, but worth every penny for a full-blown race weapon.

Q. Why are ceramic brakes silly money?

A. Ceramic brake discs are made from a compound of carbon and ceramic. The manufacturing process is complicated and lengthy, with one disc taking around a month to produce. That accounts for some of the cost. And the rest? Well, ceramic brakes are usually sold as add-ons for supercars so they're bound to be over-priced — it's not unusual to be charged three grand for an electric window on these, right?

Q. What does the DOT mean in brake fluid and what should I look for?

A. DOT is a system created by the Department Of Transport in the US to grade brake fluids based on their boiling points. DOT4 is the one you want to go for as its minimum boiling point is 230°C, more than enough for street applications. DOT5 has a higher boiling point, but it's silicone based, which isn't suitable for most braking systems.

Q. What are brake pads made of?

A. Brake pads can be made from a variety of different materials. Your standard street compound pads are usually a nonmetallic composite of various synthetic materials. They offer great cold bite and very low noise, but the drawbacks are they lack friction and will start to fade at relatively low temperatures. At the other end of the scale you have race compounds, which are either fully metallic or ceramic in composition. They offer much higher levels of friction and are a lot less susceptible to fade, but usually need warming up to optimal temperature in order to work properly. The cold bite is poor, they munch down your discs like there's no tomorrow, can be quite noisy, and you'll be lucky to get 1000 miles out of them. Great on the track, awful on the street. A good middle-ground option is a sport